What is the difference between Ki and Km in enzyme inhibition?
Posted July 22, 2020
The value Ki is the dissociation constant describing the binding affinity between the inhibitor and the enzyme, while Km is the Michaelis constant in the Michaelis-Menten equation which is used to describe the kinetics of substrate/enzyme binding. Ki is a thermodynamic parameter, reporting the true affinity an inhibitor has for binding an enzyme. In contrast, Km is a kinetic parameter, which gives the substrate concentration at which half of the maximum enzymatic reaction rate is attained. Km is determined not only by the substrate’s binding affinity, but also by how quickly the enzyme-substrate complex is turned over into product. In a rapid equilibrium where substrate binding is fast comparing to the rate at which enzyme-substrate complex turns into product, Km and Ki are identical. Whenever this assumption is not met, Km will be larger than Ki.